The problem with highly corrosive gases employed in semiconductor chambers is well documented. Some gases (for example halogen gasses such as fluorine) can corrode the internal components of the chambers. See, for example, U.S. Pat. No. 7,119,032 (incorporated herein by this reference). Disclosed in the above patent are several prior attempts to provide corrosion resistant chamber components as well as a proposal to use layered superlattice materials as a protective barrier on the surfaces of the internal components of a process chamber. See also U.S. Pat. Nos. 5,959,409; 5,810,936; 6,408,786; 6,508,911; 6,447,937; 6,830,622; 6,916,559; 7,300,537; 7,648,782; 8,357,262; U.S. and Patent Application Nos. 2009/0056626; 2011/0135915; and 2013/0122156 all of which are incorporated herein by this reference.
In U.S. Patent Application No. 2014/0178679 (also incorporated herein by this reference) proposed is an aluminum oxynitride (AlON) coating (with an optional yttria overlying coating) for process chambers. The coating is sputtered to a thickness of 1 to 10 microns. The composition is reported to be 41% Al, 57% 0, and 2% N. Potential issues with such a proposal are that the thin coating may not have a long life and thicker coating may be expensive to produce. Furthermore, thicker coatings (greater than few microns) generally have significant amounts of internal stresses which then contribute to bonding failures between the coating and the substrate. If the coating wears away to reveal the underlying substrate, the substrate is then subject to corrosion.
Also, the disclosed AlON coating is amorphous. That means it is not aluminum oxynitride with a gamma-AlON cubic spinel structure; rather it is a mixture of aluminum, oxygen and nitrogen without crystallinity for the most part. Coefficient of thermal expansion mismatch problems may also be present. Because of the low 2.0% N content, the coating could degrade at high temperature and/or could erode in the presence of corrosive gases.
Those skilled in the art have also proposed methods of making AlON bodies. U.S. Pat. No. 7,459,122 (incorporated herein by this reference) proposes a method of making AlON transparent armor. Impurities in these AlON bodies such as boron oxide, silica, titania, and the like, however, render such AlON material unsuitable for process chambers. In the process disclosed, a mixture of alumina, AlN, SiO2, and B2O3 powders are milled using high purity alumina balls.
In U.S. Pat. No. 8,211,356 (incorporated herein by this reference) by the assignee hereof, AlON powders are milled to ultimately produce polycrystalline AlON bodies proposed for ballistic armor, optical windows, and the like. Normally, high purity aluminum oxide or AlON media are not used in the milling process because such media is expensive and does not offer good wear resistance compared to less pure commercially available media. Commercially available milling media typically contains significant amounts of Si, Mg, Ca, Na, and K impurities which are then introduced into the AlON bodies. Such impurities may then contaminate the wafers processed in the process chambers.